Dilating stylet and cannula

ABSTRACT

An instrument set is provided that has a tapered configuration that facilitates the insertion of the instrument set into a patient.

RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.11/412,342, filed Apr. 27, 2006, which is incorporated by referenceherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a set of instruments having adistal tapered configuration for facilitating insertion of theinstruments into a human body.

2. Description of the Related Art

Cannulas are used in surgical procedures to access tissue of the humanbody. To assist in the insertion of the cannula into the tissue, aninstrument such as a stylet is inserted into the cannula to function asa guide for the cannula. Typically, the stylet has a diameter less thanthe diameter of the cannula, creating a stepped transition between thecannula distal end and the stylet. One problem encountered when using aconventional cannula and stylet is that the stepped transition betweenthe cannula and stylet impairs the insertion of the instruments into thesurrounding tissue because of the increased resistance encountered uponmoving the stepped transition against the surrounding tissue. Therefore,there exists a need for an instrument set having a reduced surfaceprofile in the transition between the distal end of the cannula and theinner instrument when the inner instrument extends from the distal endof the cannula so as to facilitate insertion of the instrument set intoa patient and minimize disruption to the tissue of the patient.

Another problem associated with conventional cannulated instrument setsis that the distal end of a stylet when inserted together with thecannula protrudes a distance from the distal end of the cannula that isinsufficient to optimally guide the instrument set into the surgicalsite of a patient, or optimally penetrate the tissue. Therefore thereexists a need for an instrument set that when used with a stylet, willprovide the surgeon with increased guidance for inserting the instrumentset into the surgical site of the patient while reducing the effortneeded for the instrument set to penetrate the tissue.

SUMMARY OF THE INVENTION

The present invention in one preferred embodiment includes an instrumentset with a cannula having a distal end, a proximal end, a passagetherethrough, and a mid-longitudinal axis. The passage at the distal endhas a reduced dimension transverse to the mid-longitudinal axis lessthan the maximum dimension of the passage transverse to themid-longitudinal axis. The distal end has an outer perimeter convergingat an angle toward the mid-longitudinal axis of the cannula. Theinstrument set also includes a stylet having a distal end, a proximalend, and a tapered transition portion proximate the distal end. Thetapered transition portion has an angle approximating the convergingangle of the outer perimeter of the distal end of the cannula. Thestylet is sized and configured to be inserted into the passage of thecannula. At least a portion of the tapered transition portion and thedistal end of the stylet is configured to pass through the reduceddimension of the cannula and extends beyond the distal end of thecannula.

In another preferred embodiment, the present invention includes aninstrument set with a cannula having a distal end, a proximal end, apassage therethrough, and a mid-longitudinal axis. The distal end has anouter perimeter converging at an angle toward the mid-longitudinal axisof the cannula. The instrument set also includes a stylet having adistal end, a proximal end, and a tapered transition portion proximatethe distal end. The tapered transition portion has an angleapproximating the converging angle of the outer perimeter of the distalend of the cannula. The stylet is sized and configured to be insertedinto the passage of the cannula. At least a portion of the taperedtransition portion and the distal end of the stylet is configured toextend beyond the distal end of the cannula. The instrument set furtherincludes a stop on the stylet to prevent the stylet from passing throughthe cannula.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention and together with the description, serve to explain theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of an instrument set having a cannulaand stylet in accordance with one embodiment of the present invention.

FIG. 2 is an enlarged partial side elevation view of a distal end of theinstrument set of FIG. 1 along line 2 of FIG. 1.

FIG. 3 is a partial cross-sectional side view of the distal end of thecannula of FIG. 1 with the stylet of FIG. 1.

FIG. 4 is a partial side elevation view of the distal end of the styletof FIG. 1.

FIG. 5 is a partial side elevation view of the distal end of a stylet inaccordance with another preferred embodiment of the present invention.

FIG. 6 is a partial side elevation view of the stylet of FIG. 5 rotatedapproximately 90 degrees.

FIG. 7 is a partial side elevation view of a distal end of an instrumentset having a cannula and stylet in accordance with another preferredembodiment of the present invention.

FIG. 8 is a partial cross-sectional side view of the distal end of thecannula of FIG. 7 and stylet of FIG. 1.

FIG. 9 is a partial side elevation view of a distal end of an instrumentset having a cannula and stylet in accordance with another preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings.

FIGS. 1-3 illustrate an instrument set in accordance with one preferredembodiment of the present invention. Preferably, the instrument setincludes a cannula and a stylet insertable at least in part into thecannula, the cannula and stylet each having a generally matching taperedprofile adapted to facilitate insertion of the instrument set into thetissue of a patient, preferably into the bone of a patient. It will beappreciated by those of ordinary skill in the art that the taperedprofile of the instruments set forth below may be adapted for use withother sets having two or more instruments.

As shown in FIGS. 1-3, cannula 100 is adapted to receive at least aportion of a stylet 200 therethrough. Cannula 100 includes a body 102,and exterior surface 104, a distal end 106, and a passage 108 having aninterior surface 110. Cannula 100 also includes a window 112 proximatedistal end 106. Window 112 is preferably sized and configured to permitthe passage of a portion an instrument such as a bone displacementinstrument therethrough.

Distal end 106 of cannula 100 includes an outer perimeter 114 having adistal edge 116 and may include a plurality of longitudinal serrations,grooves, or scallops 118. Serrations 118 cut into bone similar to aserrated knife. Serrations 118 preserve the strength of distal end 106because they permit the wall of cannula 100 to retain a thicknesssufficient to ensure that the distal end remains rigid while at the sametime facilitates the insertion of cannula 100 into the surroundingtissue and bone. As shown in FIGS. 2 and 3, outer perimeter 114 ispreferably tapered relative to the mid-longitudinal axis of cannula 100.The tapered portion of distal end 106 preferably includes two angledportions 120 and 122, but may include only one larger angled portion.The first angled portion 120 is preferably at an angle A relative to themid-longitudinal axis of cannula 100. A preferred range for angle A isbetween 0 to 30 degrees relative to the mid-longitudinal axis of cannula100. The second angled portion 122 is preferably at an angle B relativeto the mid-longitudinal axis of cannula 100. A preferred range for angleB is between 0 to 30 degrees relative to the mid-longitudinal axis ofcannula 100. Together, angled portions 120, 122 form a tapered profilegenerally in the range of 5 to 45 degrees, more preferably 10 to 45degrees, and most preferably 15 degrees relative to the mid-longitudinalaxis of cannula 100. It will be appreciated by those of ordinary skillin the art that outer perimeter 114 may have a single, continuous taperto distal edge 116, or more than two angled portions. It will be furtherappreciated that outer perimeter 114 may be curved in a plane parallelwith the mid-longitudinal axis of the cannula so as to approximate theshape of a spherical or elongated dome.

As shown in FIGS. 2-4, stylet 200 includes a shaft 202 and a distal end204. Shaft 202 includes a proximal portion 206, a transition portion208, and a distal portion 210 having a bevel 212 at distal end 204.Portion 210 preferably has a reduced dimension to facilitateintroduction into the tissue in a manner similar to that of a guidewire. As shown in FIG. 4, transition 208 is a tapered portion of shaft202 that converges distally toward the mid-longitudinal axis of stylet200 to provide a transition from a larger dimension of proximal portion206 to a smaller dimension of distal portion 210 of shaft 202. Theintersection of transition 208 and proximal portion 206 defines aproximal longitudinal limit 207 of transition 208. The intersection oftransition 208 and distal portion 210 defines a distal longitudinallimit 209 of transition 208. Preferably, transition 208 is at an angle Crelative to the mid-longitudinal axis of stylet 200. Angle C ispreferably in the range of 5 to 45 degrees, more preferably 10 to 45degrees, and most preferably 14 degrees relative to the mid-longitudinalaxis of stylet 200.

As shown in FIG. 3, passage 108 of cannula 100 has a reduced portionproximate distal end 106 of cannula 100 that is sized and configured tohave a transverse cross sectional dimension less than the transversecross sectional dimension of proximal portion 206 of stylet 200. Thereduced portion of passage 108 prevents stylet 200 from extending morethan a predetermined distance beyond distal edge 116 of cannula 100 bypreventing the larger dimension of proximal portion 206 of shaft 202 topass therethrough. Preferably, angle C of transition 208 of stylet 200is at an angle that is between angles A and B of cannula 100. It will beappreciated by those of ordinary skill in the art that the angles ofdistal end 106 of cannula 100 and of transition 208 of stylet 200 may bevaried without departing from the scope of the present invention.

When assembled together, the angle of the over-all tapered profiled ofouter perimeter 114 and the angle of transition 208 are each preferablywithin 15 degrees of each other, more preferably within 5 degrees ofeach other, and most preferably the same or approximately the sameangle. Additionally, when fully assembled together, distal edge 116 ofcannula 100 is adjacent transition 208 preferably between proximal anddistal longitudinal limits 207, 209 of transition 208, bothlongitudinally and along the radial height of transition 208.Preferably, distal edge 116 is closer to distal longitudinal limit 209of transition 208 more than proximal longitudinal limit 207 oftransition 208. It will be appreciated that distal edge 116 may extendbefore or after the longitudinal limits of transition 208 when thecannula and stylet are assembled to present a smooth transition withoutdeparting from the scope of the present invention.

Referring to FIGS. 1-3, in a preferred method for inserting aninstrument set such as described above into a human patient, a surgeongrasps the handle of stylet 200 (shown in FIG. 1) and places stylet 200into cannula 100 with at least a portion of transition 208 and distalend 204 of stylet 200 extending beyond distal end 104 of cannula 100. Ifdesired, the handles of the instruments may be configured to lock to oneanother with a lock 205 near the proximal end of stylet 200. The surgeonthen inserts distal end 204 of stylet 200 into the tissue such as thebone of the patient and continues advancing stylet 200, along withcannula 100, into the bone to form an opening into the bone. If desired,cannula 100 may be moved relative to stylet 200 and further advancedinto the bone using stylet 200 as a guide wire. Stylet 200 may bewithdrawn either partially or completely from cannula 100 with cannula100 remaining in the bone. Cannula 100 may be further advanced into thebone after the withdrawal of stylet 200 if desired. The instrument setis preferably inserted to a depth sufficient to permit a surgeon toaccess bone through window 112. Once stylet 200 is withdrawn, thesurgeon may insert other instruments through cannula 100, such as aninstrument to displace bone through window 112. Cannula 100 may also beused to introduce a material therethrough. Examples of materials includea flowable material such as bone cement; other therapeutic materialssuch as bone morphogenetic protein, hydroxyapatite, hydroxyapatitetricalcium phosphate, or an anti-microbial substance; or a relativelysolid and/or artificial material such as an implant.

The method is preferably performed in the spine of a human patient. Itwill be recognized that the instrument set and method of the presentinvention may be used in other areas of the human body.

Cannula 100 and stylet 200 are made of a surgical grade material.Examples of suitable materials include, but are not limited to, metalsuch as stainless steel and titanium, nitinol, carbon composites, and aplastic polymer. It will be appreciated that cannula 100 and stylet 200may be made of any combination of metal, plastic, carbon composite,nitinol, or other material suitable for the intended purpose.

In a preferred embodiment of the present invention, cannula 100 has amaximum length along the mid-longitudinal axis of the cannula that isapproximately 5.1 inches between the distal end and the handle. Thethickness of the wall of the cannula is preferably approximately 0.015inches. The maximum transverse dimension at distal end 106 of cannula100 is preferably approximately 0.1 inches. The length of the taperedportion of distal end 106 is preferably generally 0.013 inches betweenthe furthest distal extent of window 112 to distal edge 116. It will beappreciated that the dimensions set forth above may be varied withoutdeparting from the scope of the present invention.

Stylet 200 preferably has a length along the mid-longitudinal axis ofapproximately 6.1 inches between the handle and distal end 204. As shownin FIGS. 2 and 3, distal portion 210 of stylet 200 preferably has alength from the tip of distal end 204 to transition 208 that is greaterthan the length of transition 208, but less than the length of window112 of cannula 100. In a preferred embodiment, distal portion 210 ofstylet 200 has a length of approximately 0.5 inches. It will beappreciated that the dimensions set forth above may be varied withoutdeparting from the scope of the present invention.

Referring now to FIGS. 5 and 6, a stylet in accordance with anotherpreferred embodiment of the present invention is shown and referred toby the reference number 300. Stylet 300 is similar to stylet 200 exceptthat distal end 304 includes a plurality of facets 312, 314. It will beappreciated by those of ordinary skill in the art that the number andconfiguration of the facets may be varied without departing from thescope of the present invention. For example, as shown in FIG. 6, stylet300 preferably includes a plurality of facets 312, 314 at an angle toeach other. A third facet (not shown) extends on another side to form atri-faceted configuration at distal end 304 of style 300.

Referring now to FIGS. 7 and 8, a cannula in accordance with anotherpreferred embodiment of the present invention is shown and generallyreferred to by the reference number 400. As shown in FIG. 8, a cannula400 is similar to cannula 100 except that distal edge 416 of cannula 400forms a sharp edge. Additionally, outer perimeter 414 has an angledportion at an angle D which is preferably in the range of 10 to 45degrees relative to the mid-longitudinal axis of cannula 400. Angle Dhas a steeper angle as compared to angle B shown in FIG. 3. Theconfiguration shown in FIG. 8 permits a smoother transition 426 betweendistal edge 416 of cannula 400 and transition 208 of stylet 200. Thenearly seamless transition 426 further facilitates insertion of theinstrument set into the surrounding tissues of the patient at least inpart due to the reduction of the surface profile of the leading end ofthe cannula.

Referring now to FIG. 9, a cannula in accordance with another preferredembodiment of the present invention is shown and generally referred toby the reference number 500. Cannula 500 is similar to cannula 100except that body 502 includes a thread 528 proximate the distal end.Thread 528 is configured such that once the instrument set is partiallyinserted into the patient to a depth where thread 528 contacts bone, thesurgeon may rotate cannula 500 about the mid-longitudinal axis andthreadably secure cannula 500 to one or more bones of the patient.Thread 528 has a low profile thread height to allow cannula 500 to slideinto tissue without significant engagement of the thread with thesurrounding tissue. The furthest extent of thread 528 as measured alongthe mid-longitudinal axis of cannula 500 is preferably less than themaximum longitudinal extent of the tapered distal end portion of cannula500. It will be appreciated that thread 528 may be configured and placedalong the length of cannula 500 in a manner sufficient for the intendedpurpose of cannula 500. For example, as shown in FIG. 5, thread 528 ispreferably configured to engage a pedicle of a vertebra of a humanspine.

A preferred method for using the instrument set shown in FIG. 9 includesinserting by linear insertion the instrument set at least partially intothe patient through a portion of bone and tissue; inserting the set to adepth until thread 528 contacts a portion of bone, such as a pedicle ofa human spine; rotating cannula 500 about its mid-longitudinal axis toengage thread 528 within a portion of bone; and withdrawing stylet 200from cannula 500. Once the procedure has been completed through cannula500, cannula 500 is then rotated in the opposite direction of insertionto disengage cannula 500 from the bone of the patient.

The tapered configuration of the instrument set of the present inventionis applicable to a wide variety of instruments. For example and withoutlimitation, cannula 100 could be a sheath, sleeve, retractor, or anyother tubular or cannulated member. Instrument 200 could be a stylet,obdurator, trocar, bone tamp, forceps, or any other instrumentinsertable in a tube having a portion adapted to extend beyond thedistal end of the tube.

Advantages of the present invention include, for example, the ability ofthe user to more precisely place the instrument set within the patient.The tapered configuration of the present invention has the advantage ofminimizing disruption of surrounding tissues and bone as the instrumentset is being inserted into the patient. The tapered configuration of thecannula advantageously functions as a depth stop to the stylet to keepthe distal end of the stylet from extending too far beyond the distalend of the cannula. An advantage of the longitudinal serrations at thedistal end of the cannula is that the serrations facilitate insertionsimilar to a serrated knife to permit a more precise placement of theinstrument set within the patient. An advantage of the thread shown inFIG. 9 is that the surgeon is able to attach the cannula to the patientto provide a more stable base for subsequent use of instruments throughthe cannula.

It will be appreciated by those of ordinary skill in the art that thepresent invention described above may take alternative forms withoutdeparting from the scope of the present invention. For example, distalportion 210 of shaft 202 of stylet 200 may be tapered along its lengthand may, if desired, have an angle substantially matching or preciselymatching that of transition 208 to create an elongated taper. It will beappreciated that cannula 100 and stylet 200 need not have a circularcross section, but may have any other type of cross section suitable forthe intended purpose. For example, the cross section of eitherinstrument may be that of an elongated oval or other non-circular shapesuch as a square, or a shaft with a keel to prevent the inner instrumentfrom rotating within the cannula.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A surgical instrument set comprising: a cannulahaving a distal end, a proximal end, a passage therethrough, and amid-longitudinal axis, said distal end having an outer perimeterconverging toward the mid-longitudinal axis of said cannula, said distalend being sufficiently rigid to penetrate and displace bone duringadvancement of said distal end of said cannula into the bone, saiddistal end including a distal edge, said outer perimeter of said distalend of said cannula comprising a first linear portion being at a firstangle to the mid-longitudinal axis of the cannula, and a second linearportion being at a second angle to the mid-longitudinal axis of thecannula, the second angle having a value different from the first angle,the second linear portion extending from the first linear portion tosaid distal edge; and a stylet having a distal end, a proximal end, anda mid-longitudinal axis passing through said distal and proximal ends,said stylet including a handle at said proximal end of said stylet, saidhandle having an enlarged portion and a neck between said enlargedportion and said distal end of said stylet, said neck having a reducedcross-section relative to said enlarged portion and perpendicular to themid-longitudinal axis of said stylet, said stylet having a taperedtransition portion proximate said distal end, said tapered transitionportion having an angle approximating the second angle of said outerperimeter of said distal end of said cannula, said stylet being sizedand configured to be inserted into said passage of said cannula, atleast a portion of said tapered transition portion and said distal endof said stylet being configured to extend beyond said distal end of saidcannula; said neck including a stop configured to prevent said styletfrom passing completely through said cannula.
 2. The instrument set ofclaim 1, wherein the angle of said tapered transition portion and thesecond angle of said outer perimeter of said distal end are the same. 3.The instrument set of claim 1, wherein the angle of said taperedtransition portion and the second angle of said outer perimeter of saiddistal end are within 5 degrees of each other.
 4. The instrument set ofclaim 1, wherein the angle of said tapered transition portion and thesecond angle of said outer perimeter of said distal end are within 15degrees of each other.
 5. The instrument set of claim 1, wherein saidstylet has a mid-longitudinal axis and the angle of said taperedtransition portion relative to the mid-longitudinal axis of said styletis in the range of approximately 10 to 45 degrees.
 6. The instrument setof claim 1, wherein the second angle of said outer perimeter of saiddistal end relative to the mid-longitudinal axis of said cannula is inthe range of approximately 10 to 45 degrees.
 7. The instrument set ofclaim 1, wherein said tapered transition portion of said stylet isadjacent said converging outer perimeter of said distal end of saidcannula.
 8. The instrument set of claim 1, wherein said outer perimeterof said distal end of said cannula includes a plurality of serrations.9. The instrument set of claim 1, wherein said cannula has an exteriorsurface including a thread for engaging said cannula to bone.
 10. Theinstrument set of claim 1, wherein said distal end of said stylet has atip and a length as measured from said tip to said tapered transitionportion, said length being greater than the length of said transitionportion.
 11. The instrument set of claim 1, wherein the length of saiddistal end of said stylet is approximately 0.5 inches.
 12. Theinstrument set of claim 1, wherein said cannula is sized and dimensionedto pass through a pedicle of a vertebra of a human spine.
 13. Theinstrument set of claim 1, wherein said distal end of said styletincludes at least one flat surface.
 14. The instrument set of claim 1,wherein said cannula has a maximum diameter transverse to themid-longitudinal axis thereof, and wherein said stylet has amid-longitudinal axis and a maximum diameter transverse to themid-longitudinal thereof, the maximum diameter of said stylet beinggreater than one-half the maximum diameter of said cannula.
 15. Theinstrument set of claim 1, wherein the angle of said tapered transitionportion of said stylet has a value between the first angle and thesecond angle of said cannula.